"It's very hard. In these kinds of roles you're working all the time," says Marie Knowles, chief financial officer at Atlantic Richfield (ARCO), who at the age of 40 had two sons in diapers and was treasurer of the oil giant.

"My hours are long and I'm away from them a lot," says Ms. Knowles, whose sons are now in middle school. "They're fine. I'm the one who has a hard time."

"That's why women continue to carry the bigger burden," she contends. "We want to. That's part of our nature. We perceive it as part of our identity. I perceive it as part of my identity."

When Knowles is in town, breakfast and dinner are reserved for her family. "If I have to work afterward, I work at night at home," she says. Her father, who retired when her sons were born, takes them back and forth to school every day.

"You can't look to me and say, 'How did you do it Marie?'" she concedes. "Because I didn't do it alone, I did it with a lot of help."

Yet many women say it's the balancing act that keeps more women out of top corporate jobs.

"That's probably the biggest challenge we have. It's a bigger challenge than the question, 'Is there prejudice?'" says Susannah Swihart, CFO of BankBoston and a single parent. "If we choose to have children, and we have a husband with a career that has any demands to it, we have enormous challenges of trying to do it all. Some of the best of us opt out at some point along the way."

"A lot of women who are extremely successful," she adds, "don't get married, don't have children, have children who are long grown, or have a husband who has sacrificed his own career."

Many of these women credit their husbands with pulling their fair share - or more.

"I call him my secret weapon," says Deborah Hopkins, CFO at Seattle-based Boeing. "My husband is very good at saying, 'Time out. You've been [at the office] long enough. Time to come home.' "

Ms. Hopkins, who has two teenagers at home and three step-children in England, says she tries to carve out certain parts of her week just for her family.

"One of the things I've always done is to try and be there for one end of their day - either in the morning or the afternoon," she says. "I also try not to come into the office on weekends."

Yet being successful still means putting in the time.

To get to the top you have to perform at an excellent level, says BankBoston's Swihart. "I'm sorry to say this," she adds, "but at least in today's world that means being available and not very often saying, 'I can't do that.' "

As a result, many top female executives say they see the next generations of workers - women as well as men - less willing to make the same sacrifices. And many worry that the momentum women have established in the workplace could slow down.

"Unless we significantly change the way we operate in corporate America, more and more women may choose to opt out," says Boeing's Hopkins. "Let's face it, it is a huge life commitment."

"Women often say they first try to make sure they take care of their kids, and then their husband, and, of course, we all come last," Hopkins says. "It's so easy to convince yourself you don't have time."

Taking her own advice, she hired a personal trainer as part of a New Year's resolution. After her first early workout, she arrived to the office "late" - 8:30 a.m.